A new type of flexible, wearable sensor that could help people with diabetes avoid the discomfort of pin-prick blood tests, by monitoring the chemical composition of their sweat instead, has been developed by scientists at Glasgow University.

Sweat, like blood, contains metabolites, including glucose and urea. Monitoring the levels of these chemicals in sweat could help in the diagnosis and monitoring of conditions including diabetes, kidney disease and some types of cancers without blood tests.

Non-invasive, wearable systems require consistent contact with skin to provide high quality monitoring, but current products are made from rigid materials, making it more difficult to ensure consistent contact. While adhesives could offer an alternative, they can irritate skin.

Wireless systems that use Bluetooth to transmit date are also often bulky and power-hungry, requiring frequent recharging.

With funding from the European Commission and the UK’s Engineering and Physical Sciences Research Council, the Glasgow team has developed a new system built around a low-cost sensor capable of measuring pH levels, which can stretch and flex to better fit the contours of users’ bodies. It is made from a graphite polyurethane composite measuring around a square centimetre that can stretch up to 53 per cent in length without compromising its performance.

The sensor also continues to work after being flexed by up to 30 per cent 500 times. The researchers say that flexibility will allow it to be used comfortably on skin with minimal impact on the performance of the sensor.

The sensor transmits data wirelessly and without external power, to an accompanying smartphone app called SenseAble, also developed by the team. The transmissions use near-field communication, enabled in many current smartphones which is most usually used for making contactless payments. Data is transmitted via a stretchable RFID antenna integrated into the system, which is another innovation by the research team.

The smartphone app allows users to track pH levels in real time. The research was led by Ravinder Dahiya, head of Glasgow’s School of Engineering Bendable Electronics and Sensing Technologies group.

“Human sweat contains much of the same physiological information that blood does, and its use in diagnostic systems has the significant advantage of not needing to break the skin in order to administer tests,” Dahiya said.

Now the researchers have demonstrated the stretchable system can be used to monitor pH levels, they have begun additional research to expand the capabilities of the sensor and make it a more complete diagnostic system. It is planned to add sensors capable of measuring glucose, ammonia and urea, for example.

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